Apparatus and method for determining the shearing strength of a thermal insulation

ABSTRACT

The invention relates to an apparatus and method for determining the shearing strength of a thermal insulation. The apparatus ( 1 ) comprises a mobile clamping element ( 2 ) and alongside the same at least one immobile clamping element ( 3 ), each provided with a cavity ( 2   a,    3   a ) capable of receiving part of a strip-like test specimen ( 15 ) to be cut off a thermal insulation. The apparatus is adapted to apply a force F to the mobile clamping element for moving the mobile clamping element ( 2 ) relative to the immobile clamping element ( 3 ) for achieving the shearing of the presently measured strip ( 15 ) at a location ( 14 ) between the mobile clamping element ( 2 ) and the immobile clamping element ( 3 ). The apparatus is further provided with means ( 16 ) for measuring the force F for its magnitude. The method comprises cutting a thermal insulation for a strip-like test specimen ( 15 ), having certain dimensions in various directions, said strip being then placed in a measuring apparatus ( 1 ) for shearing strength. The apparatus is used for applying a force F to the mobile head for moving the mobile clamping element ( 2 ) relative to the immobile clamping element ( 3 ) for achieving the shearing of the presently measured strip ( 15 ) at a location ( 14 ) between the mobile clamping element ( 2 ) and the immobile clamping element ( 3 ), said force F being measured for its magnitude, and the shearing strength being determined on the basis thereof.

The present invention relates to an apparatus and method for determiningthe shearing strength of a thermal insulation, said thermal insulationbeing possibly manufactured e.g. from structural wool, or also frompolyurethane foam or polystyrene foam. Structural wool, i.e. so-calledhard wool, comprises a plurality of fiber layers of mineral wool, whichmake up a wool panel. Mineral wool panel can be used as such for avariety of thermal insulation applications, or it can be processed for avariety of sandwich structures, such as e.g. sandwich panels, comprisingsurface boards of e.g. plastic-coated sheet steel and a core layer ofmineral wool therebetween. Said core layer can be made directly from awool mat, the fibers lying in planes substantially parallel to thesurface boards, or for example in such a way that a mat of mineral woolis cut for lengthwise lamellae, which are turned 90° about thelongitudinal axis thereof in such a way that the fibers lie in asubstantially perpendicular relationship to the surface boards of asandwich panel. A number of lamellae are glued to each other laterallyand successively for producing a wool core of a desired size, the widthof a lamella cut from the wool mat defining the thickness of a corelayer. Thus applied, a core section made from a wool panel functions asstructural wool. In so-called lightweight sandwich elements, the coresection can be made from e.g. polyurethane or polystyrene foams insteadof structural wool. The inventive apparatus and method can also be usedfor testing a core section of such elements, as long as the core sectionis manufactured as a prefabricated unit which is then glued securely tothe surface boards of a panel.

Structural wool is subject to several different strength requirements,one being its shearing strength. Thus far, shearing strength has beenmeasured principally as defined in standard SFS-EN12090, which isnevertheless an inconvenient and slow process. The standardized methodrequires at least 30 minutes or more, as it involves waiting for theglue to dry. Hence, it is an object of the present invention to providea novel method of determining the shearing strength of structural wool,an apparatus used therein being characterized in that the apparatuscomprises a mobile clamping element and alongside the same at least oneimmobile clamping element, each provided with a cavity capable ofreceiving part of a strip-like test specimen to be cut off a thermalinsulation, said apparatus being adapted to apply a force F to themobile clamping element for moving the mobile clamping element relativeto the immobile clamping element for achieving the shearing of thepresently measured strip at a location between the mobile clampingelement and the immobile clamping element, said apparatus being furtherprovided with means for measuring the force F for its magnitude.

On the other hand, a method of the invention is characterized in thatthe method comprises cutting a thermal insulation for a strip-like testspecimen, having certain dimensions in various directions, said stripbeing then placed in a measuring apparatus for shearing strength, saidapparatus comprising a mobile clamping element and alongside the same atleast one immobile clamping element, each provided with a cavity capableof receiving part of the strip-like test specimen, said apparatus beingused for applying a force F to the mobile head for moving the mobileclamping element relative to the immobile clamping element for achievingthe shearing of the presently measured strip at a location between themobile clamping element and the immobile clamping element, said force Fbeing measured for its magnitude, and the shearing strength beingdetermined on the basis thereof.

An advantage offered by the inventive method of determining shearingstrength is that a shearing strength test can be performed quickly, asit takes no more than 2-3 minutes and, thus, can be used for continuousproduction control.

A European product standard regarding sandwich structures is underdevelopment, the chosen test method being a so-called beam test. Thebeam test comprises cutting an element for a beam about 100-200 mm wide,having a length of about 1000-2000 mm. It is good for testing a finishedproduct, but not for testing solely a core section and, moreover, it istedious and hence inapplicable to direct production control.

The invention will now be described in more detail with reference to theaccompanying drawings, in which:

FIGS. 1-3 show one exemplary embodiment for an apparatus of theinvention in schematic views from one end, from the front, and from theother end, respectively.

FIG. 4 shows schematically one inventive method of performing a shearingtest for mineral wool.

FIG. 5 shows schematically another inventive method of performing ashearing test for mineral wool.

An apparatus 1 as shown in FIGS. 1-3 comprises a frame element 4 movableon wheels 11. On top of the frame element 4 are mounted a mobileclamping element 2 and an immobile clamping element 3, which areprovided with cavities 2 a and 3 a, respectively, capable receiving atest specimen 15 cut off a mat of mineral wool. Immobility of the testspecimen is secured by means of prongs 10 in the receiving cavity ofeach clamping element. The immobile clamping element 3 remainsstationary on top of the frame element 4, while the mobile clampingelement 2 is adapted to be movable by the action of a carriage 6 alonglinear guides 7 in a vertical plane. This vertical movement isaccomplished by means of a hydraulic cylinder 5, which is connected tothe mobile clamping element 2 by way of a power sensor 16. The apparatus1 includes further a hydraulic unit 12 for producing necessary hydraulicenergy, as well as a power distribution board 13.

In operation, the strip-like test specimen 15 cut off a mat of mineralwool is placed, as shown in FIG. 4, in the receiving cavity 2 a andrespectively 3 a of the mobile element 2 and the immobile element 3,whereafter the mobile element 2 is subjected to an application force Fby displacing the mobile element 2 at a constant traveling speedrelative to the immobile element 3, whereby, as the force F increases toa sufficient magnitude, the strip 15 of mineral wool undergoes shearingat a location 14 between the mobile and immobile elements. The powersensor 16 can be used for measuring the value of force F at varioustimes and for working out the shearing strength of a mat of mineral woolfrom the maximum value force. The number of test specimens made ispreferably four, the average of shearing strength calculated from thebreaking load thereof being applied as a shearing strength value for thepresently examined mat of mineral wool. A test specimen is differentfrom a final product as there are no surface boards, resulting in acertain distortion in the value of shearing strength as compared to afinal product, but this is accommodated by using a suitable calibrationfactor determinable experimentally or mathematically.

FIG. 5 shows a method of the invention in another embodiment, comprisingtwo immobile clamping elements 3, and therebetween a mobile clampingelement 2 which is subjected to a force F for operating the samerelative to the immobile elements. A test strip 15 is placed in theapparatus in such a way that it extends into the receiving cavities ofall three clamping elements, the strip being shorn at two locations whenoperating the apparatus.

A major advantage gained by a method of the invention is the simplicityand speed of the method, which makes it possible to apply the methodalso for continuous production control. The method and apparatus aredescribed above principally in reference to mineral wool, andparticularly in reference to mineral wool used for the core section ofsandwich elements, but it is also applicable to other thermalinsulations, in which shearing strength is an important factor. Inaddition to the core section of sandwich elements, structural wool canalso be used e.g. for external heat insulation by gluing wool lamellaedirectly to a wall surface and by topping the same with a plastercoating.

1-8. (canceled)
 9. An apparatus for determining the shearing strength ofa thermal insulation, the apparatus comprising: a mobile clampingelement and at least one immobile clamping element positioned alongsidethe mobile clamping element, wherein each of the clamping elements isformed with a cavity sized to receive a portion of a strip-like testspecimen of the thermal insulation; means for applying a force to themobile clamping element thereby to move the mobile clamping elementrelative to the immobile clamping element and cause shearing of thestrip-like test specimen at a location between the mobile clampingelement and the immobile clamping element; and means for measuring amagnitude of the force.
 10. The apparatus of claim 9 comprising a singleimmobile clamping element and a single mobile clamping element.
 11. Theapparatus of claim 9, in which the at least one immobile clampingelement comprises two immobile clamping elements and the mobile clampingelement is positioned between the two immobile clamping elements. 12.The apparatus of claim 9, comprising means for operating the mobileclamping element at a constant speed, wherein a speed rate of theoperating means is variable.
 13. A method for determining the shearingstrength of a thermal insulation, comprising: cutting a thermalinsulation to obtain a strip-like test specimen; placing the strip-liketest specimen in a shearing strength measuring apparatus, the shearingstrength measuring apparatus including a mobile clamping element and atleast one immobile clamping element positioned alongside the mobileclamping element, wherein each of the clamping elements is formed with acavity sized to receive a portion of a strip-like test specimen of thethermal insulation; applying a force with the shearing strengthmeasuring apparatus to the mobile clamping element thereby to move themobile clamping element relative to the immobile clamping element andcause shearing of the strip-like test specimen at a location between themobile clamping element and the immobile clamping element; measuring amagnitude of the force; and determining the shearing strength based onthe measured magnitude of the force.
 14. The method of claim 13, inwhich the thermal insulation comprises a prefabricated core section of asandwich building element, and in which the method is used to test theshear strength of the prefabricated core section of the sandwichbuilding element.
 15. The method of claim 14, in which the prefabricatedcore section comprises structural wool.
 16. The method of claim 15, inwhich the strip-like test specimen is placed in the cavities of theclamping elements such that fibers of the test specimen are orientedsubstantially parallel to a direction along which the force is applied.